Room207's http://tesnexus.com/downloads/file.php?id=24077 has a huge selection of hairstyles, including quite a few hairs by Room himself which are designed specifically for male characters, which is rare.
There are also a lot of great hairstyles for female characters in http://tesnexus.com/downloads/file.php?id=37368. However, it is dependent on a much larger compilation (Modular Beautiful People 2chan Edition) that I don't use, so instead I have added many things from it to my own customized cosmetics mod, via the CS. It's still very much worth a look.
A lot of race mods (Mystic Elves, Corean, Saram, Sulhwa, Moonshadow Elves, Blood Witches, to name a few) include new hairstyles for use with the race- many of these are included in the mods I mention above, and made available for all races to use. Still, being handy with the Construction Set will help, should you find that you don't want quite so many options, or if you are not interested in other features of the mods, like eyes, or new races, etc.